Octave Plotting
Plotting
********
All of Octave's plotting functions use `gnuplot' to handle the
actual graphics. There are two low-level functions, `gplot' and
`gsplot', that behave almost exactly like the corresponding `gnuplot'
functions `plot' and `splot'. A number of other higher level plotting
functions, patterned after the graphics functions found in MATLAB
version 3.5, are also available. These higher level functions are all
implemented in terms of the two low-level plotting functions.
Two-Dimensional Plotting
========================
- Command: gplot RANGES EXPRESSION USING TITLE STYLE
Generate a 2-dimensional plot.
The RANGES, USING, TITLE, and STYLE arguments are optional, and
the USING, TITLE and STYLE qualifiers may appear in any order
after the expression. You may plot multiple expressions with a
single command by separating them with commas. Each expression
may have its own set of qualifiers.
The optional item RANGES has the syntax
[ x_lo : x_up ] [ y_lo : y_up ]
and may be used to specify the ranges for the axes of the plot,
independent of the actual range of the data. The range for the y
axes and any of the individual limits may be omitted. A range
`[:]' indicates that the default limits should be used. This
normally means that a range just large enough to include all the
data points will be used.
The expression to be plotted must not contain any literal matrices
(e.g. `[ 1, 2; 3, 4 ]') since it is nearly impossible to
distinguish a plot range from a matrix of data.
See the help for `gnuplot' for a description of the syntax for the
optional items.
By default, the `gplot' command plots the second column of a matrix
versus the first. If the matrix only has one column, it is taken
as a vector of y-coordinates and the x-coordinate is taken as the
element index, starting with zero. For example,
gplot rand (100,1) with linespoints
will plot 100 random values and connect them with lines. When
`gplot' is used to plot a column vector, the indices of the
elements are taken as x values.
If there are more than two columns, you can choose which columns
to plot with the USING qualifier. For example, given the data
x = (-10:0.1:10)';
data = [x, sin(x), cos(x)];
the command
gplot [-11:11] [-1.1:1.1] \
data with lines, data using 1:3 with impulses
will plot two lines. The first line is generated by the command
`data with lines', and is a graph of the sine function over the
range -10 to 10. The data is taken from the first two columns of
the matrix because columns to plot were not specified with the
USING qualifier.
The clause `using 1:3' in the second part of this plot command
specifies that the first and third columns of the matrix `data'
should be taken as the values to plot.
In this example, the ranges have been explicitly specified to be a
bit larger than the actual range of the data so that the curves do
not touch the border of the plot.
- Command: gset options
- Command: gshow options
- Command: replot options
In addition to the basic plotting commands, the whole range of
`gset' and `gshow' commands from `gnuplot' are available, as is
`replot'.
Note that in Octave 2.0, the `set' and `show' commands were
renamed to `gset' and `gshow' in order to allow for compatibility
with the MATLAB graphics and GUI commands in a future version of
Octave. (For now, the old `set' and `show' commands do work, but
they print an annoying warning message to try to get people to
switch to using `gset' and `gshow'.)
The `gset' and `gshow' commands allow you to set and show
`gnuplot' parameters. For more information about the `gset' and
`gshow' commands, see the documentation for `set' and `show' in
the `gnuplot' user's guide (also available on line if you run
`gnuplot' directly, instead of running it from Octave).
The `replot' command allows you to force the plot to be
redisplayed. This is useful if you have changed something about
the plot, such as the title or axis labels. The `replot' command
also accepts the same arguments as `gplot' or `gsplot' (except for
data ranges) so you can add additional lines to existing plots.
For example,
gset term tek40
gset output "/dev/plotter"
gset title "sine with lines and cosine with impulses"
replot "sin (x) w l"
will change the terminal type for plotting, add a title to the
current plot, add a graph of sin (x) to the plot, and force the
new plot to be sent to the plot device. This last step is
normally required in order to update the plot. This default is
reasonable for slow terminals or hardcopy output devices because
even when you are adding additional lines with a replot command,
gnuplot always redraws the entire plot, and you probably don't
want to have a completely new plot generated every time something
as minor as an axis label changes.
The command `shg' is equivalent to executing `replot' without any
arguments.
- Built-in Variable: automatic_replot
You can tell Octave to redisplay the plot each time anything about
it changes by setting the value of the builtin variable
`automatic_replot' to a nonzero value. Since this is fairly
inefficient, the default value is 0.
Note that NaN values in the plot data are automatically omitted, and
Inf values are converted to a very large value before calling gnuplot.
The MATLAB-style two-dimensional plotting commands are:
- Function File: plot (ARGS)
This function produces two-dimensional plots. Many different
combinations of arguments are possible. The simplest form is
plot (Y)
where the argument is taken as the set of Y coordinates and the X
coordinates are taken to be the indices of the elements, starting
with 1.
If more than one argument is given, they are interpreted as
plot (X, Y, FMT ...)
where Y and FMT are optional, and any number of argument sets may
appear. The X and Y values are interpreted as follows:
* If a single data argument is supplied, it is taken as the set
of Y coordinates and the X coordinates are taken to be the
indices of the elements, starting with 1.
* If the first argument is a vector and the second is a matrix,
the the vector is plotted versus the columns (or rows) of the
matrix. (using whichever combination matches, with columns
tried first.)
* If the first argument is a matrix and the second is a vector,
the the columns (or rows) of the matrix are plotted versus
the vector. (using whichever combination matches, with
columns tried first.)
* If both arguments are vectors, the elements of Y are plotted
versus the elements of X.
* If both arguments are matrices, the columns of Y are plotted
versus the columns of X. In this case, both matrices must
have the same number of rows and columns and no attempt is
made to transpose the arguments to make the number of rows
match.
If both arguments are scalars, a single point is plotted.
If the FMT argument is supplied, it is interpreted as follows. If
FMT is missing, the default gnuplot line style is assumed.
`-'
Set lines plot style (default).
`.'
Set dots plot style.
`@'
Set points plot style.
`-@'
Set linespoints plot style.
`^'
Set impulses plot style.
`L'
Set steps plot style.
`"#"'
For boxes plot style.
`"~"'
For yerrorbars plot style.
`">"'
For xerrorbars plot style.
`"~>"'
For xyerrorbars plot style.
`"#~"'
For boxerrorbars plot style.
`N'
Interpreted as the plot color if N is an integer in the range
1 to 6.
`NM'
If NM is a two digit integer and M is an integer in the range
1 to 6, M is interpreted as the point style. This is only
valid in combination with the `@' or `-@' specifiers.
`C'
If C is one of `"r"', `"g"', `"b"', `"m"', `"c"', or `"w"',
it is interpreted as the plot color (red, green, blue,
magenta, cyan, or white).
`";title;"'
Here `"title"' is the label for the key.
`+'
`*'
`o'
`x'
Used in combination with the points or linespoints styles,
set the point style.
The color line styles have the following meanings on terminals that
support color.
Number Gnuplot colors (lines)points style
1 red *
2 green +
3 blue o
4 magenta x
5 cyan house
6 brown there exists
The FMT argument can also be used to assign key titles. To do so,
include the desired title between semi-colons after the formatting
sequence described above, e.g. "+3;Key Title;" Note that the last
semi-colon is required and will generate an error if it is left
out.
Here are some plot examples:
plot (x, y, "@12", x, y2, x, y3, "4", x, y4, "+")
This command will plot `y' with points of type 2 (displayed as
`+') and color 1 (red), `y2' with lines, `y3' with lines of color
4 (magenta) and `y4' with points displayed as `+'.
plot (b, "*")
This command will plot the data in the variable `b' will be plotted
with points displayed as `*'.
t = 0:0.1:6.3;
plot (t, cos(t), "-;cos(t);", t, sin(t), "+3;sin(t);");
This will plot the cosine and sine functions and label them
accordingly in the key.
- Built-in Function: hold ARGS
Tell Octave to `hold' the current data on the plot when executing
subsequent plotting commands. This allows you to execute a series
of plot commands and have all the lines end up on the same figure.
The default is for each new plot command to clear the plot device
first. For example, the command
hold on
turns the hold state on. An argument of `off' turns the hold state
off, and `hold' with no arguments toggles the current hold state.
- Built-in Function: ishold
Return 1 if the next line will be added to the current plot, or 0
if the plot device will be cleared before drawing the next line.
- Built-in Function: clearplot
- Built-in Function: clg
Clear the plot window and any titles or axis labels. The name
`clg' is aliased to `clearplot' for compatibility with MATLAB.
The commands `gplot clear', `gsplot clear', and `replot clear' are
equivalent to `clearplot'. (Previously, commands like `gplot
clear' would evaluate `clear' as an ordinary expression and clear
all the visible variables.)
- Function File: shg
Show the graph window. Currently, this is the same as executing
replot without any arguments.
- Built-in Function: closeplot
Close stream to the `gnuplot' subprocess. If you are using X11,
this will close the plot window.
- Built-in Function: purge_tmp_files
Delete the temporary files created by the plotting commands.
Octave creates temporary data files for `gnuplot' and then sends
commands to `gnuplot' through a pipe. Octave will delete the
temporary files on exit, but if you are doing a lot of plotting
you may want to clean up in the middle of a session.
A future version of Octave will eliminate the need to use temporary
files to hold the plot data.
- Function File: axis (LIMITS)
Set axis limits for plots.
The argument LIMITS should be a 2, 4, or 6 element vector. The
first and second elements specify the lower and upper limits for
the x axis. The third and fourth specify the limits for the y
axis, and the fifth and sixth specify the limits for the z axis.
If your plot is already drawn, then you need to use `replot' before
the new axis limits will take effect. You can get this to happen
automatically by setting the built-in variable `automatic_replot'
to a nonzero value.
Without any arguments, `axis' turns autoscaling on.
The vector argument specifying limits is optional, and additional
string arguments may be used to specify various axis properties.
For example,
axis ([1, 2, 3, 4], "square");
forces a square aspect ratio, and
axis ("labely", "tic");
turns tic marks on for all axes and tic mark labels on for the
y-axis only.
The following options control the aspect ratio of the axes.
`"square"'
Force a square aspect ratio.
`"equal"'
Force x distance to equal y-distance.
`"normal"'
Restore the balance.
The following options control the way axis limits are interpreted.
`"auto"'
Set the specified axes to have nice limits around the data or
all if no axes are specified.
`"manual"'
Fix the current axes limits.
`"tight"'
Fix axes to the limits of the data (not implemented).
The option `"image"' is equivalent to `"tight"' and `"equal"'.
The following options affect the appearance of tic marks.
`"on"'
Turn tic marks and labels on for all axes.
`"off"'
Turn tic marks off for all axes.
`"tic[xyz]"'
Turn tic marks on for all axes, or turn them on for the
specified axes and off for the remainder.
`"label[xyz]"'
Turn tic labels on for all axes, or turn them on for the
specified axes and off for the remainder.
`"nolabel"'
Turn tic labels off for all axes. Note, if there are no tic
marks for an axis, there can be no labels.
The following options affect the direction of increasing values on
the axes.
`"ij"'
Reverse y-axis, so lower values are nearer the top.
`"xy"'
Restore y-axis, so higher values are nearer the top.
Specialized Two-Dimensional Plots
=================================
- Function File: bar (X, Y)
Given two vectors of x-y data, `bar' produces a bar graph.
If only one argument is given, it is taken as a vector of y-values
and the x coordinates are taken to be the indices of the elements.
If two output arguments are specified, the data are generated but
not plotted. For example,
bar (x, y);
and
[xb, yb] = bar (x, y);
plot (xb, yb);
are equivalent.
- Function File: contour (Z, N)
- Function File: contour (X, Y, Z, N)
Make a contour plot of the three-dimensional surface described by
Z. Someone needs to improve `gnuplot''s contour routines before
this will be very useful.
- Function File: hist (Y, X, NORM)
Produce histogram counts or plots.
With one vector input argument, plot a histogram of the values with
10 bins. The range of the histogram bins is determined by the
range of the data.
Given a second scalar argument, use that as the number of bins.
Given a second vector argument, use that as the centers of the
bins, with the width of the bins determined from the adjacent
values in the vector.
If third argument is provided, the histogram is normalised such
that the sum of the bars is equal to NORM.
Extreme values are lumped in the first and last bins.
With two output arguments, produce the values NN and XX such that
`bar (XX, NN)' will plot the histogram.
- Function File: loglog (ARGS)
Make a two-dimensional plot using log scales for both axes. See
the description of `plot' for a description of the arguments that
`loglog' will accept.
- Function File: polar (THETA, RHO, FMT)
Make a two-dimensional plot given polar the coordinates THETA and
RHO.
The optional third argument specifies the line type.
- Function File: semilogx (ARGS)
Make a two-dimensional plot using a log scale for the X axis. See
the description of `plot' for a description of the arguments that
`semilogx' will accept.
- Function File: semilogy (ARGS)
Make a two-dimensional plot using a log scale for the Y axis. See
the description of `plot' for a description of the arguments that
`semilogy' will accept.
- Function File: stairs (X, Y)
Given two vectors of x-y data, bar produces a `stairstep' plot.
If only one argument is given, it is taken as a vector of y-values
and the x coordinates are taken to be the indices of the elements.
If two output arguments are specified, the data are generated but
not plotted. For example,
stairs (x, y);
and
[xs, ys] = stairs (x, y);
plot (xs, ys);
are equivalent.
Three-Dimensional Plotting
==========================
- Command: gsplot RANGES EXPRESSION USING TITLE STYLE
Generate a 3-dimensional plot.
The RANGES, USING, TITLE, and STYLE arguments are optional, and
the USING, TITLE and STYLE qualifiers may appear in any order
after the expression. You may plot multiple expressions with a
single command by separating them with commas. Each expression
may have its own set of qualifiers.
The optional item RANGES has the syntax
[ x_lo : x_up ] [ y_lo : y_up ] [ z_lo : z_up ]
and may be used to specify the ranges for the axes of the plot,
independent of the actual range of the data. The range for the y
and z axes and any of the individual limits may be omitted. A
range `[:]' indicates that the default limits should be used. This
normally means that a range just large enough to include all the
data points will be used.
The expression to be plotted must not contain any literal matrices
(e.g. `[ 1, 2; 3, 4 ]') since it is nearly impossible to
distinguish a plot range from a matrix of data.
See the help for `gnuplot' for a description of the syntax for the
optional items.
By default, the `gsplot' command plots each column of the
expression as the z value, using the row index as the x value, and
the column index as the y value. The indices are counted from
zero, not one. For example,
gsplot rand (5, 2)
will plot a random surface, with the x and y values taken from the
row and column indices of the matrix.
If parametric plotting mode is set (using the command `gset
parametric', then `gsplot' takes the columns of the matrix three
at a time as the x, y and z values that define a line in three
space. Any extra columns are ignored, and the x and y values are
expected to be sorted. For example, with `parametric' set, it
makes sense to plot a matrix like
1 1 3 2 1 6 3 1 9
1 2 2 2 2 5 3 2 8
1 3 1 2 3 4 3 3 7
but not `rand (5, 30)'.
The MATLAB-style three-dimensional plotting commands are:
- Function File: mesh (X, Y, Z)
Plot a mesh given matrices X, and Y from `meshdom' and a matrix Z
corresponding to the X and Y coordinates of the mesh. If X and Y
are vectors, then a typical vertex is (X(j), Y(i), Z(i,j)). Thus,
columns of Z correspond to different X values and rows of Z
correspond to different Y values.
- Function File: [XX, YY] = meshgrid (X, Y)
- Function File: [XX, YY] = meshgrid (X)
Given vectors of X and Y coordinates, return two matrices
corresponding to the X and Y coordinates of a mesh. The rows of
XX are copies of X, and the columns of YY are copies of Y.
- Function File: meshdom (X, Y)
Given vectors of X and Y coordinates, return two matrices
corresponding to the X and Y coordinates of the mesh.
Note: this function is provided for compatibility with older
versions of MATLAB. You should use `meshgrid' instead.
Plot Annotations
================
- Function File: grid (ARG)
For two-dimensional plotting, force the display of a grid on the
plot. The argument may be either `"on"' or `"off"'. If it is
omitted, `"on"' is assumed.
- Function File: title (STRING)
Specify a title for a plot. If you already have a plot displayed,
use the command `replot' to redisplay it with the new title.
- Function File: bottom_title (STRING)
See top_title.
- Function File: xlabel (STRING)
- Function File: ylabel (STRING)
- Function File: zlabel (STRING)
Specify x, y, and z axis labels for the plot. If you already have
a plot displayed, use the command `replot' to redisplay it with
the new labels.
Multiple Plots on One Page
==========================
The following functions all require a version of `gnuplot' that
supports the multiplot feature.
- Function File: mplot (X, Y)
- Function File: mplot (X, Y, FMT)
- Function File: mplot (X1, Y1, X2, Y2)
This is a modified version of the `plot' function that works with
the multiplot version of `gnuplot' to plot multiple plots per page.
This plot version automatically advances to the next subplot
position after each set of arguments are processed.
See the description of the PLOT function for the various options.
- Function File: multiplot (XN, YN)
Sets and resets multiplot mode.
If the arguments are non-zero, `multiplot' will set up multiplot
mode with XN, YN subplots along the X and Y axes. If both
arguments are zero, `multiplot' closes multiplot mode.
- Function File: oneplot ()
If in multiplot mode, switches to single plot mode.
- Function File: plot_border (...)
Multiple arguments allowed to specify the sides on which the border
is shown. Allowed arguments include:
`"blank"'
No borders displayed.
`"all"'
All borders displayed
`"north"'
North Border
`"south"'
South Border
`"east"'
East Border
`"west"'
West Border
The arguments may be abbreviated to single characters. Without any
arguments, `plot_border' turns borders off.
- Function File: subplot (ROWS, COLS, INDEX)
- Function File: subplot (RCN)
Sets `gnuplot' in multiplot mode and plots in location given by
index (there are COLS by ROWS subwindows).
Input:
ROWS
Number of rows in subplot grid.
COLUMNS
Number of columns in subplot grid.
INDEX
Index of subplot where to make the next plot.
If only one argument is supplied, then it must be a three digit
value specifying the location in digits 1 (rows) and 2 (columns)
and the plot index in digit 3.
The plot index runs row-wise. First all the columns in a row are
filled and then the next row is filled.
For example, a plot with 4 by 2 grid will have plot indices
running as follows:
+-----+-----+-----+-----+
| 1 | 2 | 3 | 4 |
+-----+-----+-----+-----+
| 5 | 6 | 7 | 8 |
+-----+-----+-----+-----+
- Function File: subwindow (XN, YN)
Sets the subwindow position in multiplot mode for the next plot.
The multiplot mode has to be previously initialized using the
`multiplot' function, otherwise this command just becomes an alias
to `multiplot'
- Function File: top_title (STRING)
- Function File: bottom_title (STRING)
Makes a title with text STRING at the top (bottom) of the plot.
Multiple Plot Windows
=====================
- Function File: figure (N)
Set the current plot window to plot window N. This function
currently requires X11 and a version of gnuplot that supports
multiple frames.
Interaction with `gnuplot'
==========================
- Built-in Variable: gnuplot_binary
The name of the program invoked by the plot command. The default
value is `"gnuplot"'. *Note Installation::.
- Built-in Variable: gnuplot_has_frames
If the value of this variable is nonzero, Octave assumes that your
copy of gnuplot has support for multiple frames that is included
in recent 3.6beta releases. It's initial value is determined by
configure, but it can be changed in your startup script or at the
command line in case configure got it wrong, or if you upgrade
your gnuplot installation.
- Built-in Variable: gnuplot_has_multiplot
If the value of this variable is nonzero, Octave assumes that your
copy of gnuplot has the multiplot support that is included in
recent 3.6beta releases. It's initial value is determined by
configure, but it can be changed in your startup script or at the
command line in case configure got it wrong, or if you upgrade
your gnuplot installation.
- Built-in Function: graw (STRING)
Send STRING directly to gnuplot subprocess.
- Built-in Variable: gnuplot_command_plot
- Built-in Variable: gnuplot_command_replot
- Built-in Variable: gnuplot_command_splot
- Built-in Variable: gnuplot_command_using
- Built-in Variable: gnuplot_command_with
- Built-in Variable: gnuplot_command_axes
- Built-in Variable: gnuplot_command_title
- Built-in Variable: gnuplot_command_end